In the Tools toolbar, double-click on the Contour Editor button and select the Centerline Editor tool, or press Alt + W.

In the Stage view, click the contour or pencil line you want to edit near the area you wish to change.

The Centerline Editor creates a center line manipulator based on the outline's shape, with control points.

Click on one of the points to select it.

The point's Bezier handles appears, as well as Bezier handles for the surrounding points.

Do one of the following:

To move a point or a selection of multiple points, click and drag it.

To change the curve on both sides of a point, drag one of its Bezier handles.

To change the curve on only one side of a point, press and hold the Alt key, then drag one of its Bezier handles.

To deform the contour, drag a part of the contour between two points.

To deform the curve between two points, hold the Shift key and drag the contour between two points.

To remove a point's Bezier handles and make the lines it is connected to straight, press and hold the Alt key and click on the point.

Straight lines have no Bezier handles at their points by default. To create Bezier handles for these points and make their lines curved, pres and hold the Alt key, then click and hold the point and drag the mouse cursor away from it. A new Bezier handle will follow your mouse cursor until you release the mouse button.

To add a control point, press Ctrl (Windows/Linux) or ⌘ (macOS) and click on the contour where you want the new point to be created.